Doping-Induced Structural Changes of Conducting Polyalkoxythiophene on the Chemically Modified Gold Surface:  An in Situ Surface Enhanced Resonance Raman Spectroscopic Study

Abstract

In situ surface enhanced resonance Raman spectroscopy (SERRS) with excitation at 1064 nm has been used to monitor the dynamic changes in charge transfer, structure, and orientation during the redox doping of a self-assembled monolayer of conducting poly-3-(3′-thienyloxy)propanesulfonate (P3TOPS) on a gold surface modified by 2-mercaptoethylamine (MEA). The SERRS spectra were compared with Fourier transform Raman spectra of solid 3TOPS monomer and with reduced and oxidized forms of P3TOPS in solution. The oxidative doping of P3TOPS has been carried out in the potential range between -0.3 and +0.7 V, vs Ag/AgCl. Our SERRS data indicate that the oxidation process goes through initial preferential generation of polaron charge carriers with followed generation of bipolarons at higher oxidation levels. At low doping levels, thiophene rings are more coplanar than at higher ones. The observed potential dependence of the normalized integrated SERRS intensities of P3TOPS in the range of the inter-ring stretch vibrations exhibits a bell-shaped curve with a maximum at 0 V. In the potential window from -0.1 to +0.1 V, the highest number of doped coplanar neighboring molecular units is achieved. Reorientation of alkoxy side chain closer to the surface normal starts at -0.1 V. At higher potentials applied, the trans f gauche conformational transformation of the alkoxy side chain was observed along with the massive growing number of bipolarons and simultaneous deplanarization of the polymer chain.

New Insights on the Interaction between Thiophene Derivatives and Au Surfaces. The Case of 3,4-Ethylenedioxythiophene and the Relevant Polymer

“…On the other hand, stretching vibrations ascribed to methyl C–H bonds in 3-methylthiophene are well evident around 2850 cm –1 . The Raman spectra acquired employing liquid EDOT, thiophene, and 3-methylthiophene show well-evident peaks located between 2850 and 3100 cm –1 (see Supporting Information Figure S-4) ascribed to C–H stretching vibrations; in addition, the EDOT spectrum shows peaks located between 800 and 1100 cm –1 that can be ascribed to the presence of the ether moiety . However, a precise comparison between spectra acquired on Au surfaces and those acquired on pristine molecules is not at all straightforward since the positions and intensities of the different peaks could be significantly affected by the adsorption on the Au surface, also taking into account that selection rules are operative.…”

“…The adsorption of thiophenes proceeds much more slowly than previously reported for alkyl thiols, though under different experimental conditions. 38 Although a complete and reliable assignment of the vibrational spectral features of thiophene derivatives in thin films has not been reported so far, on the basis of a large number of experimental infrared and Raman spectra and theoretical calculations, 39 main assignments can be made. The major bands in the range 1350À1600 cm À1 can be attributed to the stretching vibrations of the thiophene ring.…”

Surface-Enhanced Raman Study of the Interaction of PEDOT:PSS with Plasmonically Active Nanoparticles

“…As the plasmonically active metals that are reported to enhance solar cell efficiencies are the same metals that lead to surface enhancement of Raman scattering, SERS is an obvious technique for probing the nature of the metal-conjugated polymer interaction. Prior SERS studies on organic polymer solar cell components – and other conjugated polymers ,– have not addressed the enhancement of solar cell efficiencies by SERS-active metals.…”

Electrochemical properties of mono-particle-layer films of polyaniline-coated latex microspheres

“…These applications take advantage of the electrically conducting properties. Recently, nanometer-controlled fabrication techniques have been developed to yield monolayer conducting polymer films [7][8][9], extremely thin conducting polymer wires or tubes [10][11][12][13], and conducting polymer-molecular strands connecting thin metal gaps [14,15]. The other direction in developing the fabrication techniques is to make uniform films with large areas without pinholes.…”